The goal of this project is test the feasibility of developing a broad spectrum inhibitor of multidrug transporters in gram positive pathogens. These transporters provide resistance to fluoroquinolones, currently among the most used antibiotics, by decreasing their concentration inside the bacterial cell. Inhibitors of these transporters should greatly improve the therapeutic efficacy of fluoroquinolones by not only increasing the susceptibility of gram positive bacteria to these antibiotics but also by suppressing the emergence of fluoroquinolone resistant strains. Many inhibitors of the NorA multidrug transporter in Staphylococcus aureus have already been obtained. Here, we will attempt to identify broad spectrum inhibitors, effective not only in S.aureus, but also in two other gram positive pathogens, namely Enterococcus faecalis and Streptococcus pneumoniae. First, drug- resistant strains of these two bacterial with enhanced efflux of fluoroquinolones will be selected. Second, identified NorA inhibitors will be tested for the ability to suppress efflux-mediated fluoroquinolone resistance in these strains. Third, the effect of the identified broad spectrum inhibitors on the intrinsic susceptibility of wild type S.pneumoniae and E.faecalis to fluoroquinolones and the emergence of fluorquinolone resistance in these pathogens will be evaluated. Preliminary toxicity testing and chemical improvement of the inhibitors will be performed. Finally, we will determine which fluoroquinolones currently being developed by pharmaceutical companies are subject to efflux-mediated resistance mechanisms in these bacterial species. A broad spectrum inhibitor of multidrug efflux transporters can potentially be combined with a fluoroquinolone antibiotic to form a powerful antimicrobial agent. PROPOSED COMMERCIAL APPLICATION The project is to develop broad spectrum inhibitors of multidrug efflux transporters of gram positive pathogens. These transporters provide resistance to fluoroquinolone antibiotics and thus limit their antimicrobial effects. The envisioned commercial product is a combination of such an inhibitor with a fluoroquinolone.